Atomically Precise Core Structure Evolution of High-Aspect-Ratio Silver-Alkynyl Clusters for Photothermal Conversion

The atomically precise synthesis of high-aspect-ratio metal clusters represents a promising yet challenging approach to boost photothermal performance, given that their assembly mechanisms remain poorly understood. Herein, we present a mixed-ligand synthetic route to three atomically precise silver-alkynyl clusters─[Ag 6 (RC≡C) 4 ( 3S ) 4 ](OTf) 2 (R = Ph/4-FPh, Ag 6 -H and Ag 6 -F ) and [Ag 12 (4-MeOPhC≡C) 8 ( 3S ) 6 ](OTf) 4 ( Ag 12 -OMe ), by employing substituent-engineered phenylacetylene ligands and 1,3,5-trithiane ( 3S ). Single-crystal X-ray diffraction reveals that Ag12-OMe adopts a distinctive rod-shaped Ag 12 core via directional fusion of three coplanar Ag 6 octahedra─a significant evolution from the isolated octahedral cores in Ag 6 -H and Ag 6 -F . Stability of the Ag 6 core originates from the synergistic coordination of cis -μ 3 -η 1,η 1,η 1 3S ligands and μ 3 -alkynyl ligands. By contrast, assembly of the elongated Ag 12 core is driven by μ 4 -coordination of the alkynyl ligands and argentophilic Ag···Ag interactions. Notably, Ag 12 -OMe exhibits a substantially narrowed energy gap and enhanced optical absorption. Femtosecond transient absorption (fs-TA) results indicate that the rod-shaped core significantly promotes nonradiative decay, achieving a solution-phase photothermal conversion efficiency 5.4 times higher than that of Ag 6 -H . This work provides fundamental insights into the assembly mechanism of high-aspect-ratio clusters and establishes a definitive structure–property relationship to guide the development of advanced photothermal materials.